Biaxially oriented plastic shot shell



Nov. 7, 1967 J, 5, F ET AL 3,351,014

BIAXIALLY ORIENTED PLASTIC SHOT SHELL Original Filed Feb. 7, 1962 2Sheets-Sheet 1 INVENTORS.

JOHN S METCALF CHAR E. M ER ROY LN ATTORNEY United States Patent O3,351,014 BIAXIALLY ORIENTED PLASTIC SHOT SHELL John S. Metcalf, NewHaven, Charles E. Miller, Hamden, and Roy C. Olney, North Haven, Conn,assignors to Olin Mathieson Chemical Corporation, a corporation ofVirginia Original application Feb. 7, 1962, Ser. No. 171,729. Di-

vided and this application Mar. 31, 1964, Ser. No.

3 Claims. (Cl. 10243) ABSTRACT OF THE DISCLOSURE This application isadivision of application S.N. 171,729, filed Feb. 7, 1962, nowabandoned, which is in turn a continuation-in-part of copendingapplication S.N. 135,- 569, filed Sept. 1, 1961.

. This invention relates to the manufacture of strengthened bodies ofcrystalline plastics and specifically to the manufacture of hollowbodies such as the whole case of shot shells or of other shell tubesfrom polyolefins to obtain a desired variation of structure andproperties from end to end for the purpose.

Shot shells have conventionally been made as a composite articleincluding a metal head, a tube, usually of paper, a perforated plug inthe base, and an overshot closure for the contents of shot prejec-tiles,propellant and various Wadding. As an improvement, in U.S. Patent No.2,232,634, for example, it was proposed to make a shot shell casing ofcellulose ethers or esters such as cellulose acetate together withsuitable plasticizers and fillers with the discharge end of this casingbeing sealed by fusion to a closure wad of the same material. But,because of the shortcomings of many plastics, such as embrittlement,contamination, and distortion resulting from loss of fugitiveplasticizers, and such as the lack of adequate strength, plasticconstruction has not been very successful in articles likely to be putto severe useage, particularly after long storage. With most plastics,such as the first commonly known type of polyethylene, their use in shotshells has required special modifications such as inclusion of thecollar of U.S. Patent No. 2,953,990 found to minimize the likelihood offailure in the case sidewall during firing. Especially withconventional, high pressure polyethylenes, such shells, unless they besuitably modified at added cost, tend to blow apart in the side wall andoccasionally split lengthwise even down into the head upon firing.

In an effort to overcome the disadvantage of the use of various plasticsand of separate components such as paper in shotgun shells, and in anattempt to realize the benefits of plastics such as polyethylene, thoseskilled in the art have tried the more rigid linear polyethylene. Oneapproach has been to make the entire shotgun shell casing as one piecemolded from linear polyethylene having a high degree of crystallization,a melting point of at least C. and a relatively high density. Articlesmade this may by injection molding a piece of linear polymer, however,have been found to fail at normal and low temperatures when the rate oftensile strain is high as it is in ammunition cases, at the yield point,instead of elongating and recovering for satisfactory extraction fromthe gun barrel as a sound piece. For various reasons such as thedifferences in thickness and forces encountered in various sections ofthe shell, making it by plastic injection molding even by this approachhas limitations and leaves much to be desired in obtainment of the bestcombination of physical properties.

Another approach has been to substitute a section of tube of such linearlow pressure polyethylene for the paper tube, but not until the polymerhas been oriented uniformly from end to end by stretching a tube of itto develop added strength moderately and substantially uniformly in therigid high density linear polyolefin.

It will be appreciated that ammunition cartridges are put to rigoroususe as in the firing of a shot shell case where great forces are exertedwith non-uniformity and over a wide range of temperatures. Despite thedeficiencies of paper in resisting charting and scuffing, in resistingoccasional severance from impact, in resisting dimensional change fromvariation in moisture content, in preventing absorption of moisture,many of which limit the paper shell in its capacity for re-use, variousplastic materials tried have shown disadvantages, especially afterperiods of long storage and when fired at low temperature where thedefects become exaggerated; these disadvantages have seriously precludedtheir general use for this purpose.

One object of this invention, therefore, is to provide plastic bodies ofimproved effective tensile strength together with a satisfactory elasticlimit and yield strength.

Another object is the provision of a novel process and blank for makingsuch bodies economically by deformation of a blank of plastic in thesolid state.

Another object is to provide an article composed of a crystallinepolymer of a thermo-plastic synthetic resin formed in such a way thatexceptionally high strength is obtained with desired variation adaptingthe article for use as a container under explosive pressure.

Another object is to economically form plastic articles having adequatestrength in those portions subjected to the greatest stress.

Still another object is specifically to provide a new and improvedplastic shot shell, particularly one of a suitable polyolefin.

Other objects and advantages are evident from a description of preferredembodiments, taken in connection with the accompanying drawing wherein:

FIG. 1 is an elevational view in cross section showing one embodiment ofblank or slug according to this invention;

FIG. 2 is an elevational view in cross section showing a secondembodiment of blank contemplated;

FIG, 3 is an elevational View in cross section showing a preferredembodiment;

FIG. 4 shows in cross section a portion of one suitable apparatus forprocessing the blanks to form the substantially completed shot shellalso shown in cross section; and

FIG. 5 is a graphic representation of the strength char acteristicsobtainable with reference to a typical finished cartridge case of thisinvention shown semi-diagrammatically at the foot of the representation.

In accordance with this invention, articles of manufacture, such as shotshell bodies, are formed at least in part by compression from plasticmaterials such as polyethylene, polypropylene and the like polymers,and/or co-polymers of the same, all finally shaped in the solidcrystalline state. High density linear polyolefins specifically arecontemplated for forming by compression as distinguished from forming bystretching. By confining the plastic between at least two juxtaposedsurfaces exerting pressure on the plastic and by driving plastic withplastic, final shaping to a thin-walled body is achieved advantageouslyfrom a relatively thick slug or blank of the linear polymer to attain avery high increase in strength of the body, preferably so as to increasethe tensile strength while decreasing the thickness gradually from thebase toward the mouth of the shell.

This is done at a wide range of working temperatures below thecrystalline melt temperature of the material and at speeds ofcompressive deformation limited to prevent an excessive rise intemperature, which is maintained preferably at an elevated temperaturerange less than the crystalline melt temperature. For polyethylene theworking temperatures are held well below the range from about 257 F. toabout 265 F., and working occurs preferably from about 200 F. toslightly below 265 F. for available grades and makes of thethermoplastic, Working at about 240 F. being found suitable for mostmaterials of this type. For polypropylene, the limiting temperature issomewhat higher and forming occurs below the much wider range from about275 F. to about 330335 F. Somewhat higher working temperatures fromabout 200 F. up to slightly less than 335 F. are contemplated. Bycompression forming according to this invention, shaping of an articleby deformation can occur over a broad range of temperatures below thecrystalline melt temperature rather than in a sharply limited narrowrange of temperature hovering extremely closely to such crystalline melttemperature, and difficult to maintain.

The crystalline melt temperature of thermoplastic materials such asthese is the elevated temperature at which all crystallinity of thepolymer structure disappears and it appears clear when viewed throughcrossed Nichol prisms in a hot-stage microscope. The degree ofcrystallinity, as determined by various methods such as the X- raydiffraction method, is preferably as high as possible for each material;for polypropylene a high degree of isotacticity is also preferred alongwith maximum possible crystallinity.

By compressive deformation instead of stretching, necking of thethermoplastic is avoided and very high tensile strength is obtainedwhere needed as shown in FIGURE 5. Compression forming also allows thevarious parts of the finished article also to be made to differentfinished dimensions, an advantage which is not secured when materialmust be stretched out of one part depleting it to supply another as thefinished product.

It will be appreciated that this invention is especially of advantage inmaking in one piece an article having at least two portions differing inshape and function, at least one of wide}: must be stronger than anotheror which must be thicker than other parts which nevertheless must benearly as strong or stronger. By this invention at least a superiorshell tube is formed, or preferably a superior whole shell case.

According to this invention there is provided a shot shell body 1 shownin FIGURE 4 compression shaped from a blank of polyolefin of the highdensity type, e.g. a low pressure Ziegler process type of polyethylene.

The shot shell is compression formed from a suitable blank which is aunitary piece as free as possible from discontinuities and laminations;therefore, final formation must not occur from a particulate materialdirectly. As shown in FIGURE 1, the blank is a relatively thickcylindrical slug in the form of a cup or thick walled tube 11, forexample, having central bore 12 one end of which at '15 is adapted toreceive a primer while the other is contoured as by being dished at 13to adapt this end for axial compression forming. Externally, the otherend of the tubular blank opposite the concavity 13 has a shot shell rim14 for shell extraction. At this end, corresponding to the base 20 ofthe finished shell, the exterior of the blank preferably has the shapeand size of the shell end.

Typical blanks of one type are shown in FIGURES 1 and 3, in both ofwhich the blank is substantially all plastic. Alternative to theall-plastic slug, as shown in FIG- URE 2, the slug may be a plastic core21 formed symmetrically about opening 22 to be seated in a substantiallyfinished shot shell head. This is a thin metal jacket 25 rimmed at 26and indented inwardly at the bore forming there a primer retainingflange or fingers 27 The slugs may be of various types formed in anysuitable manner preferably by injection molding carefully performed in adie to avoid the occurrence of undesired residual stresses andlamination. One end is contoured to a concavity to suit the article tobe compressively formed.

A prolate concavity such as the parabolic or hyperbolic recess 23 ofFIGURE 2 is preferred having an interior surface asymptotic ortangential to the sides of the included angle ABC of about 40 at B,i.e., an angle of from about 15 to about 25 with a side as at A and C.Preferably there is provided a blank 31, FIGURE 3, from the centralaperture 32 of which the concavity flares conically at 33 forming anangle of about 20 at the edge 36. Concentrically with opening 32 and thetapered concavity 33, the blank has rim 34 and the primer rimcountersink 35.

Each blank may be cut and machined from extruded rod and/ or tubing. Theblank of FIGURE 2 may advantageously be made by injection molding theblank directly into a rimmed metal cup 25 of final finished size liningthe injection molding die.

In apparatus for practicing the invention as shown in copendingapplication Ser. No. 135,569, filed Sept. 1, 1961, the primary parts arethe hollow die body for receiving the thermoplastic blank, the die base111 forming an abutment at one end of body 110, and the forming punch112. The punch cooperates with a reduced extension 115 for sizing theopening 112 of blank 111, for example.

According to this process, the punch is driven into the die assembly tocompress the plastic blank at speeds far below the high impact extrusionspeeds encountered in metal forming and which are capable of causingliquefaction of the material impacted, a condition avoided in theprocess.

Punch 112 has intermediate its ends a tapered outer surface 127uniformly tapered on a side at a rate of about 0.003 of an inch perlineal inch to converge toward the end 130 which in turn is nearly fiatended, beveled gradually at the corner and finally tapered more steeplyat an angle of about 20 to merge into the more gentle tapered surface127. This end forms the inner end of the hollow interior of the finishedshell 1. The die cavity converges by a uniform taper on a side at a rateof about 0.003 of an inch per lineal inch.

.In operation, by the process of this invention, a thermoplastic blank31 of No. 12 shot shell gauge and of linear high density polyethylene,for example, was placed in the die cavity after the apparatus as well asthe blank were heated through and through in any suitable manner as byimmersion to a working temperature of about 240 F. Temperature as low as70 F. have been tried but at least 200' F. is preferred. The rigidpolyethylene blank, bearing capacity does not fall off longitudinally asrapidpreferably after being given a coating of a suitable lubrily aswith plastic tubing of uniform tensile strength from cant such asethylene glycol, was then compressed. No end to end.

part of the case was subjected to drawing or stretching Improvement andvariation of strength both longitudior extrusion, as'these areconventionally practiced in the 5 nally and circumferentially is shownin FIGURE 5 in resinous plastic industry. comparison with the strengthof the untreated plastic As shown in FIGURE 4, in all instances thefinished which falls in or close to the shaded area. Adjacent thecartridge case of rigid polyolefin has projected out of the base 20, ata wall thickness of about 42 mils, a longislug a thin-walled portion 9and a rather bulky head 8 tudinal tensile yield of about 19,000 p.s.i.is attained. At of improved rigidity needed for percussive ignition. The10 the other end 16, at a thickness of about mils, this rises resultingfinished head is rigidified about primer opening to nearly 35,000p.s.i., or about ten times that of the un- 5 to final finished size bythe compressive forming opertreated linear polyethylene.

ation. Integral and concentric therewith the finished tubu- Data typicalof variation and improvement obtained lar sidewall 9 contains morehighly deformed therrnoalong the length of the shell tube 9 is indicatedin the plastic coextensive with the periphery of the slug. This 1following tabulation with reference to the representation providesadequate strength in the sidewall with desired of FIGURE 5:

TABLE Distance from base in inches 1% 1% 1% 2% 2%; 2% AV. Wall thicknessin mils 41. 8 41. 9 4 7 31. 4 28. 6 21. 7 .7 .9 Av. Tensile yieldstrength in p 10 19, 215 21, 725 25, 145 8, 800 34, 400 Load sustainedin pounds, longitu t 75 625 51 Av. Tensile yield s;rength in p.s.i.,circumferentially 5,080 5, 350 5, 720

*Measured with an Instron testing machine, Model 'lTB, at a rate of loadapplication of two inches per minute.

variation from end to end as shown in FIGURE 5, de- It will beunderstood that while this invention is parspite its being less bulkythan the head portion 8. ticularly applicable to the manufacture of shotshells, it The side wall taper in thickness was found best for is alsoapplicable to making other hollow articles of the compressive formingand best for a shot shell. The finished type open at least at one end.side wall is thickest adjacent the head and terminates in Modificationscan be made to a number of article ema thinnest part 6 at the open endwhere the shell is adapted bodiments with or without a flange and/orwith or without by this thinness for any suitable closure. Here theshell the closed end. is adapted especially for closure by in-foldingand sealing Where only an open-ended tube is desired, the blankintegrally with the rest of the shell case or any other may be reducedin height and may be otherwise suitably equivalent closure of evanescentcharacter as disclosed in modified so that in the finished product, end8 may be cut US. Patent 2,582,125 granted to R. S. Holmes. oif leavingtubular part 9 having desired variation of By this process the need forseparate heat-setting after strength over its length. treatments, suchas a dimension fixing heat treatment, is 40 A typical 12 gauge shotshell made has a head of at least avoided. 0.150 of an inch thickness atthe primer opening 5 and Head 8 has a primer receptacle 5 as well as theextracan outside diameter next the extraction rim 4 of about tion rim 4provided in the blank. 0.800 of an inch. From the 0.800 the diameter ofthe tube By the apparatus shown, it is possible to obtain desireddecreases to about 0.785 at the open end where the thickaccuracy ofconcentricity of the head and side Wall parts ness is around 0.020 of aninch. At the head the tube thickdespite the tremendous compressivepressure acting on the ness is about 0.040 of an inch. This shell ismade from a punch. thick cylindrical blank having an outer diameter ofabout While it is contemplated that articles be made accord- 0.800 of aninch, exclusive of the rim, an inner diameter ing to this inventionessentially from polyethylene, polyof about 0.230 of an inch at thebore, and a minimum propylene, other olefinic polymers and theircopolymers, height at the perforation of about that of the finished theplastic may be compounded with small amounts of opening 5 and an overallheight of about 1 or 1% inch. suitable antioxidants, coloring agents,opacifiers, and fill- Tube lengths produced are at least from about 2 to3 ers such as those described in U.S. Patent No. 2,466,038. inches.

The finished rigid polyethylene case is not only more In all embodimentsand examples, the distal end of the waterproof than a conventional papercartridge but also case remote from the base may be trimmed as necessaryfree from shrinkage and swelling as a result of moisture to provide theshape of edge desired, and dilferent from changes. The shell hasdimensional stability even over a that obtained by compressivedeformation. wide operative range of temperatures, is substantially Itwill be further understood that those skilled in the sculfproof becauseof its elasticity, and being substantially art may make other changesand modifications in the free of fugitive antioxidants and plasticizers,it does not embodiments now believed preferred Without departing changein size and pliancy. The shell being of a self-lubrifrom the spirit andscope of the invention as set forth in eating character needs noextraneous lubricant. The shell the appended claims. and its powdercharge do not suifer from migration of What is claimed is: thesecomponents. In the side wall, closure end shootolt's 1. A blank formedof a crystalline plastic material are substantially eliminated by thepermanently enhanced adapted to be deformed into a one piece shotshellcasing strength which does not diminish on aging of the shell. having atubular sidewall and greatly increased tensile Desired uniformity ofWall thickness, deformation and strength relative to the tensilestrength of said blank and strength, circumferentially is obtained.Longitudinally dean integral base at one end, said blank comprising acysired tensile yield strengths of about 19,000 to about lindrical bodyhaving an outside diameter substantially 35,000 p.s.i. are regularlyachieved with linear polyethylthe same as the diameter of the shotshellcasing to be one of the highest molecular weights, which isconsiderformed, one end of said body having a concavity formed ablyabove the strength obtained by merely injection moldtherein concentricwith the longitudinal axis of said body, ing the most rigid form of theplastic. Toward the open said concavity converging inwardly fromadjacent said one end the tensile yield strength varies upwardly so thatdeend to form an angle with the outer surface of said blank spite thedecreased thickness of the wall there, the load of from about 15 to 25.

2. A blank of crystalline olefinic material adapted to be deformed intoa one piece shotshell casing of predetermined gauge, said blankcomprising a substantially cylindrical body, a conical concavity formedat one end of said body converging toward a substantially cylindricalrimer opening formed in the other end of said body, said conicalconcavity being concentrically formed about the longitudinal aXis ofsaid body and forming a central included angle of from about 30 to about50.

3. The blank of claim 2 in which a rim formed integral with said bodyextends radially outward from said other end.

References Cited UNITED STATES PATENTS 3,093,073 6/1963 Lockwood et al10243 X 5 3,164,090 1/1965 Williams et a1 102-43 3,276,375 10/1966Larson 102-43 FOREIGN PATENTS 1,146,646 5/1957 France.

10 BENJAMIN A. BORCHELT, Primary Examiner.

ROBERT F. STAHL, Examiner.

1. A BLANK FORMED OF A CRYSTALLINE PLASTIC MATERIAL ADAPTED TO BE DEFORMED INTO A ONE PIECE SHOOTSHELL CASING HAVING A TUBULAR SIDEWALL AND GREATLY INCREASED TENSILE STRENGTH RELATIVE TO THE TENSILE STRENGTH OF SAID BLANK AND AN INTEGRAL BASE AT ONE END, SAID BLANK COMPRISING A CYLINDRICAL BODY HAVING AN OUTSIDE DIAMETER SUBSTANTIALLY THE SAME AS THE DIAMETER OF THE SHOOTSHELL CASING TO BE FORMED, ONE END OF SAID BODY HAVING A CONCAVITY FORMED THEREIN CONCENTRIC WITH THE LONGITUDINAL AXIS OF SAID BODY, SAID CONCAVITY CONVERGING INWARDLY FROM ADJACENT SAID ONE END TO FORM AN ANGLE WITH THE OUTER SURFACE OF SAID BLANK OF FROM ABOUT 15* TO 25*. 